SANAA (Reuters) - War planes from a Saudi-led military alliance bombed Yemen’s capital Sanaa on Thursday, in what witnesses described as the fiercest attacks on the city in over five months of war.

People look at the house of Brigadier Khaled al-Anduli, an army commander loyal to the Houthi movement, after it was hit by Saudi-led air strikes in Yemen's capital Sanaa September 8, 2015. REUTERS/Khaled Abdullah

The air strikes hit houses of political leaders in the Iran-allied Houthi movement and military bases, as explosions and wailing ambulance sirens forced a sleepless night on the city’s nearly 2 million shell-shocked residents.

“The sick people fled the hospital in terror,” an official at a private hospital said. “They were afraid the building would collapse from the non-stop bombing of the army bases nearby.”

There were no immediate reports of casualties, a day after medics said six civilians in the city were killed by air strikes.

Saudi Arabia and other Arab states intervened in Yemen’s civil war on March 26 to halt the nationwide spread of the Houthis, who seized Sanaa last year and forced the government into exile in Riyadh after advancing on its southern stronghold of Aden.

The Houthis, who hail from the Zaydi Shi’ite Muslim sect, consider their rise a revolution. But they are fiercely opposed by the Sunni Muslim Gulf Arab states who believe the group is bent on spreading Iran’s influence.

Since a Houthi missile attack killed at least 60 Gulf Arab troops east of Sanaa last Friday, the coalition has stepped up its air strikes on the capital and increased its deployment of troops, which Yemeni officials say number a few thousand, ahead of an eventual push towards Sanaa.

Fear is spreading that a decisive battle there may wreak widespread destruction, as it has in the southern city of Taiz, where medics said 18 people were killed in an explosion in a residential area on Thursday variously blamed on Houthi artillery shelling and Saudi-led air strikes.

Mohammed Saleh, a Sanaa resident, said he would not risk being pinned down as the bombing increases and soldiers advance.

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“I’ve decided my family and I have to get out of Sanaa. There’s nowhere left that’s safe here, and neighborhoods are getting bombed every single day.”

In the eastern port town of Mukalla, residents said three suspected al Qaeda militants were killed in an apparent drone strike on a vehicle near the airport, the latest in a string of drone attacks apparently by U.S. forces in recent months.

The Islamist militant group, exploiting the power vacuum caused by the wider war, seized control of the city in April.

Reporting By Mohammed Ghobari in Sanaa and Mohammed Mukhashaf in Aden; Writing by Noah Browning; Editing by Sami Aboudi and Robin Pomeroy